The invention relates to a local area network comprising a plurality of sub-networks and a plurality of bridge terminals, which bridge terminals are each provided for transmitting data between the terminals of at least two sub-networks via a wireless medium.
Such a local area network comprising a plurality of sub-networks is known from DE 196 37 026 A1. A sub-network contains a plurality of terminals which exchange via a radio transmission medium (wireless medium) cells generated in the asynchronous transfer mode. Data are transmitted between two sub-networks via a bridge terminal. How a bridge terminal, after being put into operation, finds two sub-networks between which data can be exchanged via the bridge terminal is not further explained.
It is an object of the invention to provide a bridge terminal for connecting at least two sub-networks in a local area network, which bridge terminal, after being put into operation, automatically connects sub-networks for the data exchange.
The object of the invention is achieved by a local area network of the type defined in the opening paragraph, in that a bridge terminal after being put into operation, is provided for determining the sub-networks that can be reached, for establishing a list of groups that have each n elements as an identification for the sub-networks, from all the m sub-networks that can be reached, where m greater than n and n greater than 1, for sorting the groups in the list according to a predefined criterion, and for connecting the sub-networks whose identification is stated in the first group of the sorted list.
According to the invention, a bridge terminal, after being put into operation, determines all the sub-networks that can be reached. A certain identification is then determined which features the respective sub-network. Such an identification may be, for example, a property of a sub-network. A property of a sub-network may be the channel group that is used by the terminals for data transmission and is assigned to the sub-network. A channel group is understood to mean a number of certain channels which are assigned to each sub-network of the local area network for data exchange. The channel is determined by a frequency range, a time range and, in addition, by a spreading code.
After m sub-networks have been detected, a list is made up of certain groups. A group contains n elements. An element is used as an identification for a sub-network. The number of the n elements is to be smaller than the number of the m sub-networks (m greater than n) and n should exceed 1 (n greater than 1), since at least two sub-networks are to be interconnected. For example, a group may contain two elements or identifications and thus form a pair. This means that a bridge terminal is provided for connecting two sub-networks.
The list is sorted in accordance with a predefined criterion. When the bridge terminal uses the channel group assigned to a sub-network as an identification, the bridge terminal can form the sum of the received average energies for each set of channel groups and sort the sets according to the reduction of the calculated sums. Alternatively, it is possible for the bridge terminal to determine the receiving quality of a control message sent by the controller for each set of channel groups and to sort the sets according to the degrading receiving quality. After the sorting operation, the bridge terminal connects the sub-networks whose identification is stated in the first group of the sorted list.
A bridge terminal receives an identification of the sub-network from a sub-networks terminal designated as a controller. Such a controller is at least responsible for control and management functions in the sub-network.
When a bridge terminal interconnects only two sub-networks and no loop is formed in the entire local area network, the transfer of data can be effected very simply in a bridge terminal. A loop in the local area network means that a sub-network may receive data of another sub-network not only from one but from at least two bridge terminals. A bridge terminal then performs only simple operations under the said requirements. A bridge terminal needs to have only the information which of the two sub-networks received data are to be sent to.
If data are received from the first sub-network, whose receiver can also be reached via the first sub-network, the bridge terminal will erase the data. If the data from the first sub-network are to reach a receiver that can be reached via the second sub-network, the bridge terminal will send the data to the second sub-network. The data from the first sub-network may originate either from a terminal or a controller of the first sub-network or from a terminal or controller of another sub-network. The bridge terminal connecting the second sub-network, for example, to a third sub-network, may similarly convey the data to the third sub-network, if necessary.
For a bridge terminal that interconnects only two sub-networks, it is only necessary to know via which of the two sub-networks the receiver of the data can be reached. It is not necessary for the bridge terminal to store information about the actual location of the receiver and the transmission paths to this location.
The information as to which sub-network a bridge terminal is to send received data comes from broadcast messages transmitted by a newly registered terminal. This broadcast message contains at least the identification number of the terminal. With the identification number the bridge terminal stores to which sub-network data for the terminal are to be transmitted. This is the sub-network that has transmitted the respective broadcast message to the bridge terminal. If a bridge terminal connects only two sub-networks, not only the identification number, but also one extra bit is to be stored for the two connected sub-networks.
If a bridge terminal has detected as a loop, a connection to two sub-networks is attempted whose identifications belong to the next group of the sorted list. By transmitting a loop test message, a bridge terminal detects whether there is a loop. If after a certain period of time the loop test message does not come back to the bridge terminal that has transmitted the loop test message, there is no loop. This loop test message may be repeated several times for reasons of safety.
The bridge terminal contains a radio device having at least a high-frequency circuit, a modem and a protocol device and a radio switching device. The radio switching device controls the exchange of data between the sub-networks and the protocol device the connection between at least two sub-networks.
The data transmitted in the local area network may be generated, for example, in accordance with a packet transfer method. The packets may be transmitted via the wireless medium as a whole or as sub-packets after the addition of further data. The wireless transmission is understood to mean a radio, infrared or ultrashell transmission etc. For example, the asynchronous transfer mode (ATM), which generates fixed-length packets called cells, may be used as a packet transfer method.
The invention further also relates to a bridge terminal of a local area network that has a plurality of sub-networks and further bridge terminals for transmitting data between the terminals of at least two sub-networks via a wireless medium.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.